This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Recent developments in applied mathematics have yielded an analytic Green's function to the Boltmann Transport Equation (BTE) which provides an exact description for photon migration in turbid media. The use of a Green's function rather than Monte Carlo simulations promises to model important problems with much less computational expense. We are investigating approaches to utilizing this solutions to address important forward and inverse problems of photon migration in homogeneous and heterogeneous tissues using this approach. We are also working on incorporating the Green's function based ERT kernel into the Solver module of the Virtual Tissue Simulator.